boost program_option配置文件的不区分大小写分析

我想使用boost::program_options从配置文件中读取选项,允许不区分大小写的解析。

例如,考虑以下简单代码:

#include <iostream>
#include <fstream>
#include <string>
#include <boost/program_options/options_description.hpp>
#include <boost/program_options/parsers.hpp>
#include <boost/program_options/variables_map.hpp>

int main()
{
  using namespace std;
  namespace po = boost::program_options;

  ifstream inputfile("input.dat");
  po::options_description desc("");
  desc.add_options()
    ("l", po::value<unsigned int>())
    ;
  po::variables_map vm;
  po::store(po::parse_config_file(inputfile, desc), vm);
  po::notify(vm);

  if (vm.count("l"))
    cout << "l is set as " << vm["l"].as<unsigned int>() << endl;
  else
    cout << "l is not set";

  return 0;
}

有以下几点 input.dat 文件

l=3

程序运行良好,输出良好

l is set as 3

如果我换了 输入输出 作为

L=3

程序终止引发异常

terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::program_options::unknown_option> >'
  what():  unrecognised option 'L'
Aborted

显然可以在命令行上进行不区分大小写的解析,请参见讨论 here . 是否也可以使用case-insentive解析来读取配置文件?